What is the most POWERFUL engine you have ever been behind?

23,648 if all you are talking about is HP. I have about 8,000 hours in C-130E models. Thay are powered by 40Allison t-56 Turboprop jet engines with 5,912 Shaft HP each. Although technically, I was not behind the engines. If you are talking about a car, I had a ride on a racetrack with a well prepped Viper. WOW! The most powerful car I have ever driven was when my oldest daughter paid for me to attend one of those NASCAR driving experience things. My 69 Barracuda has about 370 HP.